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Phylum Platyhelminthes
April Adams
Zoology NCHS
Phylum Platyhelminthes• Flat worms• Triploblastic= 3 germ
layers• Acoelomate• Bilateral symmetry• Hermaphroditic• 1 opening for digestion• Simple nervous and
muscular systems• Flame cells• May be free living or
parasitic• CEPHALIZATION
AcoelomateAcoelomate
EctodermMesodermEndoderm
Digestive cavity is the only inner cavity, and is not lined with mesoderm.
Phylum Platyhelminthes: Class Turbellaria
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Acoelomate
Other Body Plans:PseudocoelomateOther Body Plans:Pseudocoelomate
EctodermMesodermEndodermFluid filled cavity between the endoderm and ectoderm- pseudocoelom
Differs from a true coelom because…. • It is not entirely lined with mesoderm tissue• Organs are not suspended or attached to membranes
(mesenteries)
Other Body Plans:Coelomate
Other Body Plans:Coelomate
EctodermMesodermEndoderm
Mesoderm lines cavity between digestive tract and body wall
8
Flatworm Body Systems
• No Circulatory or Respiratory systems- simple diffusion through body wall
Systems Present-• Digestive• Nervous • Reproductive• Excretory
Flatworm Body Systems:Digestive
Incomplete-• mouth • pharynx (to swallow
food) • Gastrovascular cavity• intestine(no anus)
Nervous System
Lateral nerve cord
Eye spot= detects light
anterior ganglia
transverse nerve cord
sensory receptors
Cephalization=“Primitive Brain”Cephalization=“Primitive Brain”
Auricle
Cerebral ganglion
Pairednerve cords
Excretory System
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- Gets rid of nitrogenous wastes
- protonephridia- first kidney
Components:- Flame cells- Excretory
ducts/tubes- pores
Reproductive System • Sexual and asexual
reproduction sexual- eggs + sperm asexual- regeneration
• Hermaphrodites- both male (penis and testis)
and female organs(vagina and ovary)
16
Checkpoint1. Which phylum do flatworms belong to?2. Flatworms are triploblastic, what does that mean?3. What type of body cavity do they have? Explain.4. Flatworms are the “first” of many things in the animal
kingdom. What traits do flatworms display that were not present in Poriferans, Cnidarians, or Ctenophores?
5. Flatworms have the first excretory system. How does it work?
Kingdom AnimaliaPhylum PlatyhelminthesClasses:
TurbellariaTrematodaCestoda
Class Turbellaria
• Most free-living• Aquatic• Eye spots• Regenerate if cut
in two• Ex. Planaria
Planarians
• Lives in fresh water usually under leaves and rocks
• Usually feeds on dead or slow moving organisms
Planarian Reproduction
Reproduction:• Sexually:
hermaphrodites
• Asexually: can regenerate missing body parts (called fission)
What would happen ????
Detaches its tail end and each half regrows the lost parts
each Planaria gives and receives sperm
Planarians: body structures• Nervous/sensory system: Brain-like structure• Nerve cord: carries impulses down body• Eyespots: sense light and dark• Sensory pits: line sides of head to aid in
movement and sensing surroundings
Planarians: body structuresDigestive/excretory system• Mouth: located in center of
ventral side• Pharynx: tube like structure
which extends from mouth during feeding; acts like a straw sucking up food and carrying it to body
• Food enters mouth and solid wastes exit mouth
• Flame Cells: remove excess water and nitrogenous wastes
eyespot
ganglion
Gastrovascular cavity
Mouth pharynx
Flame cells
ganglion
Nerve cord
(15:00 Sea of Life- Planarian clip)
Class Trematoda• Trema= “hole”• Holdfast devices
– Endoparasites• Complex life cycle- larval
stage in one or more hosts
Primary host-juvenile/larva stage-
Secondary host- adult stage
Ex. Blood and liver flukes
FlukesBlood fluke life cycle:• Eggs are released in water
from wastes of infected host• Hatch in to swimming larvae
in water• Larvae enter a primary host
(like a snail) where they develop & mature to Cercaria stage
• Enter water again and bore into skin of secondary host (man)
• From the blood stream they bore into intestines where they attach and feed on blood
Schistosoma
• Blood flukes• 200 million people• 1 million deaths/year
Life Cycle of a Schistosome Fluke
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Schistosome
• Cercaria have forked tail
Swimmers Itch
Clonorchis sinensis
Oral sucker
Intestine
Uterus
Yolk gland
Testes
Ovary
Seminal recepticle
Clonorchis sinensis
• Chinese liver fluke• 50 million people• Cirrhosis of liver• Diarrhea• Edema• Pain
Fasciola hepatica
• Sheep liver fluke• Sheep, cattle and
man– Weight loss
• Eat contaminated vegetation
Life Cycle of the Sheep Liver Fluke
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Paragonimus westermani
• Lung fluke• Carnivores, pigs,
rodents and man• May be fatal
Class Cestoda: “cess pool”
• Tape worms• All parasitic• Live in intestines of
vertebrates• No digestive system• 40 feet long
Tapeworm structures• Scolex= “head”• hooks and suckers to
aid in attachment to intestine
• Proglottids: individual parts of worm- reproductive– Each one is detachable– Each proglottid may
contain up to 100,000 eggs which fall off when full
– When released, they exit with the host’s wastes
gonad
Tapeworm life cycle• Cows consume contaminated
vegetation, Eggs hatch in intestines of intermediate host (pig or cow)
• Young worms burrow out of intestine into cow’s muscle tissue forming cysts
• Secondary host (man) eats undercooked/raw meat containing worm larvae cysts
• Larvae hatch and mature in intestines, soak up digested food of host
• Proglottids mature, eggs released with feces
• Eggs attach to plant to form cysts
Scolex
Proglottid
Uterus
Testes
Ovary
Yolk gland
Vas deferens
Seminal receptacle
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Pork Tapeworm (Taenia solium)
Taenia saginata
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Source: Redrawn From Centers for Disease Control, Atlanta, GA.
Life Cycle of the Broad Fish Tapeworm
Diphyllobothrium latum
Dipylidium caninum
Echinococcus granulosus
• Parasite of dogs– Host
• Juveniles in sheep, man and other mammals– Intermediate host
• Hydatid cyst
Hydatid Cyst
• Cysticercus – Juvenile stage
• Adult stage in dog
Ecinococcus granulosus
50
Checkpoint
1. What are the three classes of flatworms?
2. Which class contains free living species?
3. How do planarians consume food?
4. How are flukes different from Planarians?
5. How are tapeworms different from Trematodes?